Usually, the Lawful Good types go for Chaotic Evil mates. They know they their love can change their mates. The Chaotic Evil mates goes for it because the Lawful Good type is hot and the sex is good. If the Lawful Stupid is unlucky, he or she dies naked and alone after some passion in the wilderness. With luck, the Evil Overlord's plan will result in the Chaotic Evil mate's death, ensuring the mate's betryal of the Evil Overlord. If he is really lucky, the Evil Overlord's hechmage will have planted a failsafe that will kill her if she doesn't lt the good guys magically change her alignment to Chaotic Good.

I point to Silverbolt and Blackarachnia, the only Wolf-Bird Paladin and Black Widow Spider Assasin bioroid couple ever to have an implied sex scene on daytime children's television.

I think I got the reason right here: Lawful Stupid Sir Parrish vs. Garkenlot
http://snltranscripts.jt.org/01/01kvalour.phtml

In one of The Agenda episodes, I think. It requires some imagination but there is a scene that could be interperated as post coital. It could easily be interperated other ways as well, but I remember thinking that they had just had sex when I saw it.

Ahem.